public class Solution {
    public int mySqrt(int x) {
        if (x == 0) {
            return 0;
        }
        int start = 1;
        int end = x;
        while (start + 1 < end) {
            int mid = (end - start) / 2 + start;
            if (mid < x / mid) {
                start = mid;
            } else if (mid == x / mid) {
                return mid;
            } else {
                end = mid;
            }
        }
        return start;
    }
}